Mass spectrometer tube ion source assembly



Dec. 6, 1949 A. o. c. NIER 2,490,278

MASS SPECTROMETER TUBE ION SOURCE ASSEMBLY Filed Oct. 51, 1947 /NVENTORAL FRED O.C. N152.

Patented Dec. 6, 1949 MASS SPECTROMETER TUBE ION SOURCE ASSEIWBLY AlfredO. C. Nier, Minneapolis, Minn, assignor to Regents of the University ofMinnesota, Minneapolis, Minn., a corporation of Minnesota ApplicationOctober 31, 1947, Serial No. 783,433

3 Claims. (Cl. 25041.9)

This invention relates to improvementsin mass spectrometer tubes and thelike and particularly to improvements in the ion source portion thereof.Heretofore, mass spectrometer tubes have been so constructed that theion source is not readily removable once the tube is completed for thisportion of the tube must, in common with the remainder of the tube, bede-gassed by application of heat and pumping before the tube is set intooperation. Hence, the constructions heretofore used have not beenreadily accessible, and such opening provisions as have been made arecumbersome to a degree that servicing the ion source has been adifficult and time consuming operation.

It is an object of the invention to provide an improved massSpectrometer overcoming these objections of prior constructions and toprovide an ion source which is readily accessible, easily serviced andeasily put into operation.

Other objects of the invention include the provision of an improved unitconstruction of an ion source for a mass spectrometer tube, capable ofassembly or disassembly from the tube proper.

Other and further objects of the invention are those inherent in theapparatus herein illustrated, described and claimed.

The invention is illustrated in the drawings in which Figure 1 is avertical transverse sectional view of the apparatus of the presentinvention;

Figure 2 is a vertical transverse sectional view taken in the directionof arrows 2-2 of Figure 1.

Throughout the drawings corresponding numerals refer to the same parts.

In the drawings certain of the lead wire connections within the tubeproper have been omitted for purposes of clarity.

Referring to the drawings the mass spectrometer tube proper is composedof a metallic tube, such as Inconel or other nonmagnetic tubing I whichis sweat soldered at II into a terminal flange I2. so as to present atight fit to the external surface of the tube to which it is soldered.The upperportion of the flange is provided with a flange I3 which seatsin a groove I6 in the mating flange I of the ion source assemblygenerally designated 20. The ion source includes the flange I5 whichserves as an assembly base for all of the remaining elements of the ionsource. The flange I5 has the same external diameter as the flange I2and. is apertured so that it can be fastened to the flange I 2 by meansof a plurality of cap screws 2 I evenly spaced around the periphery ofthe flange. A locating pin 53 mounted on one of the flanges The flangeis recessed at the joint II" and a cooperating hole in the other flangeinsures re-assembly in one position only. The flange I5 is provided withan internal step 22 upon which a plate 23 is centrally fastened andattached by Soldering at the surface 24. The outer diameter of the plate23 is such as to leave an internal groove in which a peripheral gasketI4 which is capable of maintaining a gas-tight high vacuum joint isseated, The tongue flange I3 of the mass spectrometer tube flange I2 isadapted to reach into the groove and seat upon the gasket I 4 when thetwo flanges I2 and I5 are drawn together by the screws 2I and thusprovide an exceedingly tight joint. The tongue I3 has a sufiicient axialdimension so that when it is seated upon the gasket I 4 a space remainsbetween the two flanges as at 25. This facilitates the separation of twoflanges for servicing.

The flange I5 has a central aperture and has a step 26 milled in theupper surface so as to receive the end of a tube 28 which is soldered tothe flange I5 at the step 26. The tube 28 is capped at 29, and cap 29carries the internally extending metallic tube 30 which is sealed ingastight relation to the glass squash 3| through which eight lead-inwires pass in gas-tight relationship at the squash portion 32. The leadwires are, respectively, J 1, J2, J3, D, S, T, F1 and F2. In thedrawings these are shown broken off at the line 33 for purposes ofclarity, but it will be understood that they extend downward to thecorresponding connections at breaking line 33'. The plate 23 also servesto support four stainless steel posts, of which posts 34, 35 and 36 areshown in the drawings.

The four posts are spaced in rectangular configuration and are fastenedby screws or brazing to the plate 23. When the ion source is assembledas shown in Figures 1 and 2,

the posts 34 extend into the tube II] of the mass spectrometer tube andserve to support the elements of the ion source which are showngenerally opposite the bracket 38.

The ion source consists of a plurality of spaced: plates S, S, J1, J2,J3, D and ground plates G1, G2

and G3, together with a deflection plate D. Plates S and S (which areconnected together) and plates J1, J2, J3 and D are mounted on wireposts 39, 40 and M which extend from the stainless steel posts 35, 35,36 etc. All of these plates are insulated from each other and from theposts. Plates G1, G2 and G3 are likewise mounted on the posts but arenot insulated therefrom since they are all at ground potential, the sameas the posts. The spacing of the plates J1, J2, J3, G1, G2, G3, and D isby means of glass washers pocket and are connected to thecorrespondinglead wires F and F entering through the squash of the tube.

The filament F is hair pin shaped and its apex,

which is most intensely heated, is adjacent. an, aperture in wall 44 sothat a beam of electron,

emitted by the filament passes through the aperture in the direction ofa corresponding aperture in the wall 45 and after passing therethrough'enters an antrum formed by the U-shaped chan nel T which is insulatedfrom but mounted on wire 4i and connected by a suitable. insulated leadwire, not illustrated, to the correspondingly nu m bered wire. Tentering through the squash, A

potential is maintained between the filament F and the antrum plate T(which is known as the trap) and the electrons are accordingly drawnacross the space between walls 44.and 45.

In the spacebetween walls 44 and 45 thereis a rectangular pocket whichis connected by a. tube- 49, thence through the couplings 59 and andthroughsthe hole 52 to the inlet capillary tube 53, through which. thegas sample to be analyzed is,

introduced into the spectrometer tube. The mole-.

cules of gas in the sample to be analyzed are thus conducted directly tothe space defined by the walls 42, 43, 44 and and the molecules in .this

space aresubjected to a beam of electrons from the filament F whichpasses through the aperture.

in plate 44, thence across. the space and through the aperture in theplate 45to the trap T. The

electrons bombard the molecules and causethem to be ionized, hence to besubject to acceleration potentials.

The lower plate S in Figures 1 and} has an aperture slit at its centralportion and below the lower plate S are a plurality of plates J1, J2 andJ3. Potential supplies of gradually increasing value (more positive) areconnected to the plates J1J3, respectively. Ground potential is appliedto plates G1, G2 and G3. Plates J1 and Jaare half platesand define aslit between them. Plate J3 is a full plate and has a slit in thecenter. The

potentials so applied. to plates J1, J2 and J3 form a field whichreaches through the slit in the lower plate S and the ionized and hencecharged molecules are accelerated by the potential gradient and passthrough the slits defined by the plate S and by the plates J1 and J2 andby plate J3, the ionized molecules attain a gradually increasingvelocity and upon leaving the slit defined by the full plate. G1, themolecules continue to move along (or coast) at a velocity determined bythe potential gradient through which they haye fallen. Thus, in aspecific installation ground po tential is applied tov plates G1, G2 andG3 and positive. potentials applied to the plates J 1, J2, J3 and S. asfollows: J3=1700 volts plus; J1 and Jz=1800 volts plus; and S= 0O0 voltsplus. The stream of ionized molecules is indicated by the dotted line Mand is subject to some focusing action due to the particular potentialsapplied :to the lates J1 through J3.

The ionized molecules move towards. the first ground plate G1, and afterpassing through a slit therein, pass through the space formed by the T-shaped ground plate G2 and the T-shaped deflector plate D. Normally theplate D is connected :to ground and hence normally (during the operationof the mass spectrometer tube), the ionized molecules continue in theirmovement through the slit plate G3 and thence on throughthernassspectrometer tube. When it is desired to turn off the massspectrometer tube, this is conveniently done by applying a positivepotential to the plate D which causes the ionized molecules to bedeflected and miss the slit in the plate G; and hence are collected onthe plate G3. It will be understood that the plates S-S, J 1, J2, J3, G62, Ge, D and-the filament terminals are con nected to thecorrespondingly designated lead-in wires entering through the squash 32.

At the junction of the mass spectrometer tube liland the flange l2-thereis soldered a full turn of copper tubing and similarly at the junctionof the flange l5 and thetube 28 there is soldered another full turn oftubing 5]. These tubesg50 and El may be connected in series andcoolingwater is run through them when the assembly has been madeand the massspectrometer tube is be:

pumped out. Durin the pumping operation W it is necessary todegas. Thisis accomplished by vigorously heating the entire assembly by a gas torchor by a high frequency. furnace applied around the ionsource assembly orby other types of electric furnaces. The heating thus accomplished wouldseriously deteriorate the gasket l4 by the passage of cooling waterthrough the tube s 5 0,an d 5|.

The entire assembly of theion source is mo unted, upon the flange l5which, as. previously described, is usually removable from the flange12. Therefore, for purposes of constructing the ion source, flange. l5forms a handy mounting plate upon which the delicate. elements supportedby the posts 34, 3,5, 36 etc. can bemounted, fastened the. flange l2, ofthe mass spectrometer tube proper arid once the cap screws 2 l-.2.l arepulled down tight a gas-tight junction is perfected at the sealinggasket I4. The pin 54 provided. in one or the other of the flanges I2 orI5 seats in a corresponding aperture of the opposite flange. Thispermits assembly of the flange. [5 in only one position of the flangel2, and hence the ion source may be. readily removed and as readilyre-mounted upon the. mass spectrometer tube without fear that adjustmentof the ion source axially of the mass spectrometer tube will be lost.The easy removability ofthe ion source assembly permits replacement ofthe filament F ina few minutes time in the event it burns out andreadily permits adjustment of the remaining elements of the. ion source.should this be neces- Plate D, J1 or J2 can be used for interrupting thebeam in order. to change the ion current from a steady D. C. to apulsating D. C. current. In some cases it is more desirable to use A. C.amplifiers to measure the analyzed currents, and deflecting plates suchas D, J1 or J2 may be used to modulate the beam if an alternating orpulsating potential is applied to one of the three.

As many apparently widely different embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that I do not limit myself to the specific embodiments hereinexcept as defined by the appended claims.

What I claim is:

1. In a mass spectrometer having an elongated tube portion terminatingat the ion source, the improvements comprising a first flange mounted ingas-tight relationship on said tube, a unitary ion source and gas inletstructure including a thick second flange for removable attachment ingas-tight relationship to the first flange, a plurality of mountingposts on the second flange and positioned and spaced so as to extendaxially into the elongated spectrometer tube when the flanges arecoupled together, a filament, sample bombardment chamber, electron trapand ionized molecule accelerating and focusing plates mounted as anassembly on said posts, all of said parts being thereby carried on thesecond flange, a squash inlet also mounted in gas-tight relation on thesecond flange, and a sample inlet extending axially through said thicksecond flange and connected by a sample inlet conduit to the samplebombardment chamber.

2. The apparatus of claim 1 further characterized in that one of theflanges is provided with a subsidiary circumferential tongue and theother flange is provided with a cooperating mating groove in which agasket is seated.

3. The apparatus of claim 2 further characterized in that said gasket'isformed of a material which deteriorates'upon the application of heatthereto and a circular cooling fluid tube is soldered to the exteriorsurface of each flange, said tubes being in thermal communication withthe gasket retained between said flanges whereby said flanges and gasketmay be cooled during general heating of the assembly for degassing.

ALFRED O. C. NIER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name: Date 1,118,380 Story Nov. 24, 19141,353,976 Stoekle Sept. 28, 1920 1,690,232 Kuhn Nov. 6, 1928 2,378,962Washburn June 26, 1945 2,417,797 Hipple Mar. 18, 1947 OTHER REFERENCESCoggeshall and Jordan, Review of Scientific Instruments, May 1943, vol.14, pp. 125-129.

